DC-to-DC converters convert an DC input voltage to a DC output voltage of a different amount. The DC output voltage is compared with a reference voltage to perform switching control based on the comparison results. This stabilizes the DC output voltage at a desired level. In general, a reference voltage is generated by a reference voltage source. The reference voltage source is typically driven by the DC output voltage.
For example, the technology can apply to charging a capacitor, a secondary battery or the like by applying to a DC-to-DC converter a minute voltage generated by a solar battery or thermo-element as a DC input voltage, and converting the DC input voltage to a DC output voltage by the DC-to-DC converter. However, the DC-to-DC converters may fail to apply a driving voltage with a level sufficient for the reference voltage source to initiate an operation. In this case, the operation of DC-to-DC converters may be unstable since they cannot use a required reference voltage.